Antigens in moldy hay as the cause of farmer's lung

Diagnosis of Fibrotic Hypersensitivity Pneumonitis: Is There a Role for Biomarkers?

Hypersensitivity pneumonitis is a complex interstitial lung syndrome and is associated with significant morbimortality, particularly for fibrotic disease. This condition is characterized by sensitization to a specific antigen, whose early identification is associated with improved outcomes. Biomarkers measure objectively biologic processes and may support clinical decisions. These tools evolved to play a crucial role in the diagnosis and management of a wide range of human diseases. This is not the case, however, with hypersensitivity pneumonitis, where there is still great room for research in the path to find consensual diagnostic biomarkers. Gaps in the current evidence include lack of validation, validation against healthy controls alone, small sampling and heterogeneity in diagnostic and classification criteria. Furthermore, discriminatory accuracy is currently limited by overlapping mechanisms of inflammation, damage and fibrogenesis between ILDs. Still, biomarkers such as BAL lymphocyte counts and specific serum IgGs made their way into clinical guidelines, while others including KL-6, SP-D, YKL-40 and apolipoproteins have shown promising results in leading centers and have potential to translate into daily practice. As research proceeds, it is expected that the emergence of novel categories of biomarkers will offer new and thriving tools that could complement those currently available.

Hypersensitivity pneumonitis

The lung is constantly exposed to a wide variety of environmental insults. In its defense against these environmental challenges, however, the lung responds through a limited number of pathophysiologic mechanisms. This is well illustrated by a group of diseases which are collectively referred to as hypersensitivity pneumonitis. This syndrome includes a very large number of different diseases. However, in the United States, only farmer's lung, bird-breeder's lung, and ventilation hypersensitivity pneumonitis occur with any significant frequency. Each of these is characterized by flu-like symptoms, in conjunction with a pneumonitis consisting of lymphocytic granulomatous infiltration of the alveoli and terminal bronchioles. This disease is caused by the inhalation of antigenic material which usually originates from the dusts of organic material. A host of different dusts and antigens have been described in conjunction with hypersensitivity pneumonitis but each leads to the same characteristic clinical syndrome. Thus, each of the diseases shares similar clinical features but differs primarily with respect to the nature of the exposure and causative antigens. The clinical features, pathogenesis, course, prognosis, and treatment of these related diseases are reviewed.

Investigation of human immune response to Micropolyspora faeni antigens by enzyme-linked immunoelectrodiffusion assay and immunoblotting

Immune response to Micropolyspora faeni was analyzed in 10 patients suffering from farmer's lung by two techniques: enzyme-linked immunoelectrodiffusion assay (ELIEDA) and immunoblotting. ELIEDA revealed the presence in all patients of various specific immunoglobulin G (IgG), IgM, IgA, and IgE antibodies, with the number of arcs ranging from 4 to 19. M. faeni proteins were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and immunoblotted with human sera and specific immunoglobulin-peroxidase conjugates. In immunoblotting, the predominant immunoglobulin class was IgG for all patients. At least 20 bands ranging from 15,000 to 60,000 in molecular weight were observed in a highly positive serum, whereas IgM- and IgA-specific reactivity was directed mainly to the 28,000- and 49,000-molecular-weight bands; M. faeni-specific IgE antibodies appeared less often. The rheumatoid factor (IgM-RF), which also had high titers in these patients (greater than 1/512), interfered with ELIEDA, while only slightly interfering with the immunoblotting detection of specific IgM. This latter technique provided a better characterization of immune response in patients with farmer's lung than ELIEDA did and should also permit discrimination of recently exposed individuals from chronic patients. Moreover, this technique should make it possible to determine whether the response of one particular immunoglobulin class to an antigen fraction can be associated with a specific state of the disease.

Characterization of Micropolyspora faeni antigens

Culture filtrate antigens of Micropolyspora faeni grown in a synthetic medium in a stirred fermentor were characterized. The culture filtrate antigens were fractionated by preparative isoelectric focusing with a pH gradient of 3.5 to 5.5. The fractions were pooled according to their reaction with rabbit anti-M. faeni sera. A pool containing two major antigens which were resolved by analytical isoelectric focusing and polyacrylamide disc gel electrophoresis was obtained. One antigen was stainable with Coomassie blue and periodic acid-Schiff stain and was determined to have a mass of 51,000 daltons. The other antigen was stainable only with Coomassie blue and was determined to have a mass of 29,000 daltons. When used at 1 mg/ml, this pool reacted with the sera from all patients with farmer's lung disease by immunodiffusion but failed to react with control sera.

Micropolyspora faeni and farmer's lung disease

Several methods were used to obtain serologically active materials from cultures of Micropolyspora faeni. From the results of immunodiffusion and immunoelectrophoresis tests on these materials it is suggested that preparations for the laboratory diagnosis of farmer's lung disease (FLD) should contain concentrated culture supernatant (CS) and extracts of mycelium obtained by ultrasonic treatment (MU). Although CS and MU have many serological activities in common they also possess activities unique to each.Extraction of mycelium with trichloracetic acid, boiling water or methanol yielded a product which gave simple patterns in immunodiffusion tests. The products contained little protein but were rich in carbohydrates, particularly arabinose, galactose and glucosamine. A similar material was obtained from a cell-wall preparation by treatment with lysozyme. Antibodies to the serologically active substances in these materials occurred more frequently in sera of patients with FLD than antibodies to any other M. faeni antigen.Attempts to obtain serologically active materials from spores were unsuccessful. Moreover antibodies to M. faeni could not be removed from patients' sera by absorption with partially purified spore preparations. It is suggested that the hypersensitivity in FLD arises from exposure to mycelial antigens.

Farmer's lung. A clinical, radiographic, functional, and serological correlation of acute and chronic stages

In assessing patients suffering from farmer's lung, the acute stage must be distinguished from the chronic stage of the disease. The conspicuous radiographic signs in the acute farmer's lung episode and the often dramatic clearing make an important contribution to the diagnosis. The radiographic changes in chronic farmer's lung are not specific and cover a wide range of appearances. Even minor nodular changes are significant. Farmer's lung, acute and chronic, is not a disease predominantly characterized by a defect in gas exchange. During the acute illness the reduction in diffusing capacity is often accompanied by a decrease in lung volumes; the pulmonary function profile of the chronic stage is variable. In only a relatively small proportion of chronic farmer's lung patients does a defect in gas exchange predominate, and in some it may be manifest only during exercise. Airway obstruction is a feature of chronic farmer's lung. In chronic farmer's lung patients discrepancies between the severity of complaints and results of pulmonary function tests are not infrequent. In some patients with considerable disability conventional pulmonary function studies may demonstrate little or no impairment of the functions measured. In patients suffering from an acute farmer's lung episode, serological tests should be positive, possibly in high titre. In the chronic stage of the disease the chance of finding positive serology in a patient diminishes with the length of time elapsed since the last acute episode. The period of serological transition appears to be the third year.